Conventionally, in the graphic art field, processing solution waste generated along with the wet process for image forming materials has caused problems regarding workability, and in recent years, a decrease in the processing solution waste has been strongly demanded in terms of ecological concerns and space savings. Thus, a technique for a light heat photographic material for technical photographic use is sought in which exposure can be effectively carried out using a laser image setter, and development by no use of processing solution, is possible, so that sharp and bright images with high resolution can be attained.
Methods for such techniques are well known and which are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,487,075, and in D. Morgan, "Dry Silver Photographic Materials" (Handbook of Imaging Materials, Marcel Dekker, Inc. page 48, 1991), etc.
Said thermally developable photosensitive material comprises a reducible silver source (organic silver salt), a light catalyzer with a catalytically active amount, and a reducing agent which are generally dispersed into a (organic) binder matrix. The thermally developable photosensitive material is stable at normal temperatures and is developed, after exposure, when heated to high temperatures. Upon heating, silver is formed through an oxidation-reduction reaction between the organic silver salt (functioning as an oxidizing agent) and the reducing agent. This oxidation-reduction reaction is accelerated by the catalytic action of a latent image formed in the silver halide through exposure. Silver formed by the reaction with the organic silver salt in an exposed area yields a black image, which contrasts with unexposed areas to form a visual image.
In order for the thermally developable photosensitive material to be effectively exposed to produce an excellent dot image, a photosensitive material, by which a high contrast image can be obtained, is necessary. A conventional silver halide photosensitive material contains a hydrazine derivative as a high contrast enhancement agent, and it is well known that the above-mentioned thermally developable photosensitive material also contains a hydrazine derivative as described in U.S. Pat. Nos. 5,545,505 and 5,464,738.